A spectrum that can be used in an orthogonal frequency division multiplexing (OFDM) system is divided into a plurality of subcarriers, and each subcarrier can bear different data amounts according to a condition of a transmission channel. Therefore, after the OFDM system is started, a set of handshake and initialization mechanisms need to be established between a central office end and a terminal to perform protocol negotiation, channel discovering training and reference exchange. A data service interworking stage can be entered only after these stages are finished.
When the channel training is performed between the central office end and the terminal, usually, a terminal device (the central office end or the terminal) sends a series of initialization signals with a specified power spectrum to a receiving device (the terminal or the central office end), and the receiving device evaluates a bearing capability of each subcarrier according to the spectrum of the received signal, so as to obtain an evaluation about a data communication capability in this direction. In addition, in an initialization process of the channel training, the terminal device needs to uninterruptedly send specified initialization signals to the receiving device, and if an interruption occurs in the middle of the sending, the receiving device cannot detect a signal and therefore offline occurs, that is, in the initialization process, the terminal device needs to process initialization signals uninterruptedly, and software resources and hardware resources of the terminal device cannot be used for other computations.